The present invention relates to methods useful in subterranean operations, and more particularly, to methods of enhancing the conductivity of fractures in subterranean formations.
Fracturing treatments are commonly used in subterranean operations, among other purposes, to stimulate the production of desired fluids (e.g., oil, gas, water, etc.) from a subterranean formation. For example, hydraulic fracturing treatments generally involve pumping a treatment fluid (e.g., a fracturing fluid) into a well bore that penetrates a subterranean formation at a sufficient hydraulic pressure to create or enhance one or more cracks, or “fractures,” in the subterranean formation. “Enhancing” one or more fractures in a subterranean formation, as that term is used herein, is defined to include the extension or enlargement of one or more natural or previously created fractures in the subterranean formation. The creation and/or enhancement of these fractures, among other things, may enhance the flow of fluids through the subterranean formation, which may be produced out of the subterranean formation (e.g., into and out of a well bore penetrating at least a portion of the subterranean formation) more readily. The rate of flow of fluids through a portion of a subterranean formation is referred to herein as the “conductivity” of that portion of the formation. Such fracturing treatments also may be performed in combination with other subterranean treatments useful in the particular formation, such as gravel packing and/or acidizing treatments, which may be referred to as “frac-packing” and “frac-acidizing” treatments, respectively.
In order to maintain and/or enhance the conductivity of a fracture in a subterranean formation, particulates (often referred to as “proppant particulates”) may be deposited in the open space of the fracture, for example, by introducing a fluid carrying those proppant particulates into the subterranean formation. The proppant particulates may, inter alia, prevent the fractures from fully closing upon the release of hydraulic pressure, forming conductive channels through which fluids may flow to the well bore. Once at least one fracture is created and the proppant particulates are substantially in place in the fracture, the treatment fluid carrying the proppant particulates may be “broken” (i.e., the viscosity of the fluid is reduced), and the treatment fluid may be recovered from the formation. The process of placing proppant particulates in a fracture is referred to herein as “propping” the fracture. Although it is desirable to use proppant particulates in maintaining the conductivity of a fracture, the propped fracture should remain sufficiently permeable to allow the flow of fluids therethrough.
A displacement fluid also may be used in a subterranean formation that comprises one or more fractures, inter alia, to displace the fracturing fluid into the formation and/or to move the proppant particulates into the open space of the fracture. For example, the displacement fluid may be pumped into the subterranean formation immediately after the fracturing fluid to move the proppant out of the well bore into the open space of the fracture. The use of the displacement fluid may, inter alia, allow the proppant particulates to be placed deeper within the fracture than with the use of a fracturing fluid alone, which may enhance the conductivity of the fracture.
However, conventional methods of using displacement fluids in propped fractures may be problematic. If the proppant particulates in a propped fracture are displaced too far into the subterranean formation, they may be moved away from the near-well bore area, where the proppant particulates may not be able to hold open fractures so as to remain in communication with the well bore. This may allow the fracture to close, which can obstruct the conductive flow path through the fracture to the well bore and may decrease the production of fluids from the well.